Standard air to air or liquid heat exchanger core assemblies (radiators, oil coolers, charge air coolers, or the like) include two aluminum/header plates, two inserts (side panels or plates) and a stack of aluminum tubes and fins all braised together. An issue with this design is tube failure occurs due to thermal stress. When vehicles are operated in cold weather, the heat exchanger radiator is subjected to high temperature gradients. Thus, one part of the radiator is very hot, while the other part is cold. This results in high tube stresses. This is due to the core expanding/contracting at different rates. Also, due to the rigidity of the core or header plates, there is little, if any, thermal relief between the tubes.
Different types of designs have been proffered to deal with thermal stress. Some designs add tube stiffeners inside the tube to increase the bending moment of inertia at the tube header joint. Other designs have utilized high strength magnesium tubes to increase the fatigue life of the tube. Additionally, inserts are cut to enable thermal relief at the corner tubes. However, several issues are associated with each of the proffered solutions.